Currently, silicone oil, wax, talc, mica, tetrafluoroethylene resin, and other mold-releasing agents are used in the molding of polymeric materials, such as plastic materials and rubber materials, using molds. Although silicone oil, wax, etc., have excellent mold releasability, such mold-releasing agents are transferred to molded products, thereby impairing the uniform coating properties, secondary processability, etc., of the molded products; in addition, durability is not sufficient. As for tetrafluoroethylene resin, the durability of mold release effect and secondary processability are satisfactory; however, it is necessary to perform bake treatment to form a film on the molding surface of a mold in the mold-release treatment, and the same treatment is required for retreating. Consequently, many treating processes are required.
In order to solve these defects, mold-releasing agents comprising a C4-C20 polyfluoroalkyl group-containing phosphoric acid ester as one of their active ingredients are proposed (see Patent Documents 1 to 3). These mold-releasing agents exhibit excellent mold releasability and have a longer mold release life than conventional mold-releasing agents; however, due to the recent trend toward the more complicated shape of molded products, there is a demand for mold-releasing agents having much higher performance.
Polyfluoroalkylethyl phosphonic acid esters are also widely used as starting materials for the synthesis of mold-releasing agents. Compounds having a C8-C12 perfluoroalkyl group are most likely to develop mold release performance when used as mold-releasing agents. In particular, phosphonate compounds having a perfluorooctyl group and represented by the formula:CF3(CF2)7CH2CH2P(O)(OC2H5)2 are preferably used in this kind of application (see Patent Documents 4 to 7).
Incidentally, it is reported that telomer compounds having a C8-C12 perfluoroalkyl group are biologically degraded in the environment and converted to compounds having relatively high bioaccumulation and environmental concentration, causing concerns for exposure during treatment processes, and for release or diffusion from waste, treated substrates, etc., into the environment. Moreover, compounds having a perfluoroalkyl group containing 14 or more carbon atoms are very difficult to handle because of their physical and chemical properties, and hence, such compounds are rarely used in practice.
Furthermore, as for telomer compounds having a perfluoroalkyl group containing 8 or more carbon atoms, generation and mixing of perfluorooctanoic acids with high bioaccumulation potential is unavoidable during the production process of these compounds. For these reasons, companies that produce such telomer compounds have retreated from the production of the compounds or promoted the use of alternative compounds having a perfluoroalkyl group containing 6 or less carbon atoms.
However, compounds having a perfluoroalkyl group containing 6 or less carbon atoms cause a significant decrease in orientation on the surface of a treated substrate, and the melting point, glass transition point (Tg), etc., of the compounds are markedly lower than those of C8 compounds. Accordingly, the compounds are highly influenced by their using environmental conditions, such as temperature, humidity, stress, and contact with organic solvents. Consequently, the desired performance cannot be sufficiently achieved, and durability and other properties are affected.
An aqueous mold-releasing agent composition in which an ammonium salt or amine salt of perfluoroalkylalkyl phosphonic acid and polyether-modified organopolysiloxane are dissolved or dispersed in water is also proposed (see Patent Document 8). Perfluorooctylethyl phosphonic acid salt is also used in this case, and a transparent mold releasing agent solution is obtained.
Moreover, perfluoropolyether oils widely used as water- and oil-repellents, lubricants, etc., have excellent water- and oil-repellency and lubricity; however, due to the lack of compatibility with other compounds, they have limited application.
There is an attempt to use a perfluoropolyether oil as a leather-treating agent by adding thereto a fat-liquoring agent (see Patent Document 9). In the general description, phosphonic acid derivatives having a fluoroalkyl group, fluoroalkenyl group, or fluoroether group, or ammonium salts, alkali metal salts, or alkaline earth metal salts thereof are referred to as examples of the fat-liquoring agent, and the fat-liquoring agent is used at a weight ratio of 10 to 0.5, preferably 5 to 1, relative to the fluorine-based oil.
Patent Document 9 indicates that the fluorine oil and fat-liquoring agent used at such a weight ratio are generally used as a leather-treating agent contained in the form of emulsion, and the leather-treating agent is used to treat tanned leather in the fat-liquoring process. As for the treating agent rich in the fat-liquoring agent, the average particle diameter of the emulsion is lower in proportion to the amount of emulsifier used, and stability over time is ensured; however, because of the excessive content of the hydrophilic fat-liquoring agent, the material to be treated becomes hydrophilic to reduce water-repellency. Further, when this is used as a mold-releasing agent, reduction of mold releasability is unavoidable (see Comparative Example 3, described later).
The present applicant has previously proposed a method for producing perfluoroalkylethyl phosphonic acid by pyrolysis or hydrolysis of perfluoroalkylethyl phosphonic acid diester (see Patent Document 10). The perfluoroalkylethyl phosphonic acid obtained by this method is not dissolved in an aqueous medium, such as water, and therefore cannot be used as an emulsifier aqueous solution, etc.
On the other hand, perfluoropolyether oils can be used as surface-treating agents by forming them into emulsions, and can be applied to mold-releasing agents.
However, although emulsions as described in Patent Document 9, in which an excessive amount of fat-liquoring agent (ammonium salt or metal salt of perfluoroalkylalkyl phosphonic acid) is mixed with fluorine-based oil, the emulsions can be suitably used in a leather treatment method, when the perfluoropolyether oil emulsion is applied as a mold-releasing agent, the mold releasability of these compounds themselves is not sufficiently exhibited.